Cycles rendering double question: render quality and render time
For interior scenes, I find that using portals can work well. Set up an area lamp in a window facing into the room. Set it to portal, and set up another opposite of it on the other side of the scene. 
I also turn off caustics in my render settings, set light bounces no higher than 6-8 in most cases unless the first render just doesn't look right, and set my tile size to 16 x 16 to 18 x 18. Granted, I am using CPU, so this is more efficient for me I have found. For fireflies, I also set indirect clamp to a minimum of 1.01